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			<h1>JavaScript <span class="color_h1">运算符</span>
</h1>
<hr>
<p><strong>运算符 = 用于赋值。</strong></p>
<p><strong>运算符 + 用于加值。</strong></p>

<hr>
<p>运算符 = 用于给 JavaScript 变量赋值。</p>

<p>算术运算符 <span class="marked">+</span> 用于把值加起来。</p>


<div class="example">
<h2 class="example">实例</h2>
	<p class="example">指定变量值，并将值相加：</p>
<div class="example_code">
<div class="hl-main"><span class="hl-identifier">y</span><span class="hl-code">=</span><span class="hl-number">5</span><span class="hl-code">;
</span><span class="hl-identifier">z</span><span class="hl-code">=</span><span class="hl-number">2</span><span class="hl-code">;
</span><span class="hl-identifier">x</span><span class="hl-code">=</span><span class="hl-identifier">y</span><span class="hl-code">+</span><span class="hl-identifier">z</span><span class="hl-code">;</span></div>
</div>
<p>在以上语句执行后，<em>x</em> 的值是：</p>
<div class="example_code">
7
</div>
<br><a target="_blank" href="../try/try.php?filename=tryjs_operators1" class="tryitbtn" rel="noopener">尝试一下 »</a>
</div>
<br><hr>
<h2>JavaScript 算术运算符</h2>
<p算术运算符用于执行变量<strong>与/或</strong>值之间的算术运算。
</p>
<p给定<strong> y=5</strong>，下面的表格解释了这些算术运算符： </p>

<table class="reference">
<tr>
<th width="13%" align="left">运算符</th>
<th width="32%" align="left">描述</th>
<th width="15%" align="left">例子</th>
<th width="15%" align="left"> x 运算结果</th>
<th width="15%" align="left"> y 运算结果</th>
<th width="10%" align="left">在线实例</th>
</tr>
<tr>
<td valign="top">+</td>
<td valign="top">加法</td>
<td valign="top">x=y+2</td>
<td valign="top">7</td>
<td valign="top">5</td>
<td valign="top"><a target="_blank" class="tryitbtn" style="float:right;width:55px;padding-top:0px;padding-bottom:1px" href="../try/try.php?filename=tryjs_oper_add" rel="noopener">实例 »</a></td>
</tr>
<tr>
<td valign="top">-</td>
<td valign="top">减法</td>
<td valign="top">x=y-2</td>
<td valign="top">3</td>
<td valign="top">5</td>
<td valign="top"><a target="_blank" class="tryitbtn" style="float:right;width:55px;padding-top:0px;padding-bottom:1px" href="../try/try.php?filename=tryjs_oper_sub" rel="noopener">实例 »</a></td>
</tr>
<tr>
<td valign="top">*</td>
<td valign="top">乘法</td>
<td valign="top">x=y*2</td>
<td valign="top">10</td>
<td valign="top">5</td>
<td valign="top"><a target="_blank" class="tryitbtn" style="float:right;width:55px;padding-top:0px;padding-bottom:1px" href="../try/try.php?filename=tryjs_oper_mult" rel="noopener">实例 »</a></td>
</tr>
<tr>
<td valign="top">/</td>
<td valign="top">除法
</td>
<td valign="top">x=y/2</td>
<td valign="top">2.5</td>
<td valign="top">5</td>
<td valign="top"><a target="_blank" class="tryitbtn" style="float:right;width:55px;padding-top:0px;padding-bottom:1px" href="../try/try.php?filename=tryjs_oper_div" rel="noopener">实例 »</a></td>
</tr>
<tr>
<td valign="top">%</td>
<td valign="top">取模（余数）</td>
<td valign="top">x=y%2</td>
<td valign="top">1</td>
<td valign="top">5</td>
<td valign="top"><a target="_blank" class="tryitbtn" style="float:right;width:55px;padding-top:0px;padding-bottom:1px" href="../try/try.php?filename=tryjs_oper_mod" rel="noopener">实例 »</a></td>
</tr>
<tr>
<td valign="top" rowspan="2">++</td>
<td valign="top" rowspan="2">自增</td>
<td valign="top">x=++y</td>
<td valign="top">6</td>
<td valign="top">6</td>
<td valign="top"><a target="_blank" class="tryitbtn" style="float:right;width:55px;padding-top:0px;padding-bottom:1px" href="../try/try.php?filename=tryjs_oper_incr" rel="noopener">实例 »</a></td>
</tr>
<tr class="fixzebra">
<td valign="top">x=y++</td>
<td valign="top">5</td>
<td valign="top">6</td>
<td valign="top"><a target="_blank" class="tryitbtn" style="float:right;width:55px;padding-top:0px;padding-bottom:1px" href="../try/try.php?filename=tryjs_oper_incr2" rel="noopener">实例 »</a></td>
</tr>
<tr style="background-color:#ffffff">
<td valign="top" rowspan="2">--</td>
<td valign="top" rowspan="2">自减</td>
<td valign="top">x=--y</td>
<td valign="top">4</td>
<td valign="top">4</td>
<td valign="top"><a target="_blank" class="tryitbtn" style="float:right;width:55px;padding-top:0px;padding-bottom:1px" href="../try/try.php?filename=tryjs_oper_decr" rel="noopener">实例 »</a></td>
</tr>
<tr style="background-color:#ffffff">
<td valign="top">x=y--</td>
<td valign="top">5</td>
<td valign="top">4</td>
<td valign="top"><a target="_blank" class="tryitbtn" style="float:right;width:55px;padding-top:0px;padding-bottom:1px" href="../try/try.php?filename=tryjs_oper_decr2" rel="noopener">实例 »</a></td>
</tr>
</table>
<br><hr>
<h2>JavaScript 赋值运算符</h2>
<p>赋值运算符用于给 JavaScript 变量赋值。
</p>
<p>给定 <strong>x=10 </strong>和<strong> y=5</strong>，下面的表格解释了赋值运算符：</p>

<table class="reference notranslate">
<tr>
<th width="13%" align="left">运算符</th>
<th width="32%" align="left">例子</th>
<th width="20%" align="left">等同于</th>
<th width="25%" align="left">运算结果</th>
<th width="10%" align="left">在线实例</th>
</tr>
<tr>
<td valign="top">=</td>
<td valign="top">x=y</td>
<td valign="top"> </td>
<td valign="top">x=5</td>
<td valign="top"><a target="_blank" class="tryitbtn" style="float:right;width:55px;padding-top:0px;padding-bottom:1px" href="../try/try.php?filename=tryjs_oper_equal" rel="noopener">实例 »</a></td>
</tr>
<tr>
<td valign="top">+=</td>
<td valign="top">x+=y</td>
<td valign="top">x=x+y</td>
<td valign="top">x=15</td>
<td valign="top"><a target="_blank" class="tryitbtn" style="float:right;width:55px;padding-top:0px;padding-bottom:1px" href="../try/try.php?filename=tryjs_oper_plusequal" rel="noopener">实例 »</a></td>
</tr>
<tr>
<td valign="top">-=</td>
<td valign="top">x-=y</td>
<td valign="top">x=x-y</td>
<td valign="top">x=5</td>
<td valign="top"><a target="_blank" class="tryitbtn" style="float:right;width:55px;padding-top:0px;padding-bottom:1px" href="../try/try.php?filename=tryjs_oper_minequal" rel="noopener">实例 »</a></td>
</tr>
<tr>
<td valign="top">*=</td>
<td valign="top">x*=y</td>
<td valign="top">x=x*y</td>
<td valign="top">x=50</td>
<td valign="top"><a target="_blank" class="tryitbtn" style="float:right;width:55px;padding-top:0px;padding-bottom:1px" href="../try/try.php?filename=tryjs_oper_multequal" rel="noopener">实例 »</a></td>
</tr>
<tr>
<td valign="top">/=</td>
<td valign="top">x/=y</td>
<td valign="top">x=x/y</td>
<td valign="top">x=2</td>
<td valign="top"><a target="_blank" class="tryitbtn" style="float:right;width:55px;padding-top:0px;padding-bottom:1px" href="../try/try.php?filename=tryjs_oper_divequal" rel="noopener">实例 »</a></td>
</tr>
<tr>
<td valign="top">%=</td>
<td valign="top">x%=y</td>
<td valign="top">x=x%y</td>
<td valign="top">x=0</td>
<td valign="top"><a target="_blank" class="tryitbtn" style="float:right;width:55px;padding-top:0px;padding-bottom:1px" href="../try/try.php?filename=tryjs_oper_modequal" rel="noopener">实例 »</a></td>
</tr>
</table>
<br><hr>
<h2>用于字符串的 + 运算符</h2>
<p>+ 运算符用于把文本值或字符串变量加起来（连接起来）。</p>

<p>如需把两个或多个字符串变量连接起来，请使用 <span class="marked">+</span> 运算符。</p>

<div class="example">
<h2 class="example">实例</h2>
<p class="example">如需把两个或多个字符串变量连接起来，请使用 <span class="marked">+</span> 运算符：</p>
<div class="example_code">
<div class="hl-main"><span class="hl-identifier">txt1</span><span class="hl-code">=</span><span class="hl-quotes">&quot;</span><span class="hl-string">What a very</span><span class="hl-quotes">&quot;</span><span class="hl-code">;
</span><span class="hl-identifier">txt2</span><span class="hl-code">=</span><span class="hl-quotes">&quot;</span><span class="hl-string">nice day</span><span class="hl-quotes">&quot;</span><span class="hl-code">;
</span><span class="hl-identifier">txt3</span><span class="hl-code">=</span><span class="hl-identifier">txt1</span><span class="hl-code">+</span><span class="hl-identifier">txt2</span><span class="hl-code">;</span></div>
</div>
<p> <em>txt3</em> 运算结果如下:</p>
<div class="example_code">
What a verynice day</div>
<br><a target="_blank" href="../try/try.php?filename=tryjs_operators2" class="tryitbtn" rel="noopener">尝试一下 »</a>
</div>


<p>要想在两个字符串之间增加空格，需要把空格插入一个字符串之中：</p>

<div class="example">
<h2 class="example">实例</h2>
<div class="example_code">
<div class="hl-main"><span class="hl-identifier">txt1</span><span class="hl-code">=</span><span class="hl-quotes">&quot;</span><span class="hl-string">What a very </span><span class="hl-quotes">&quot;</span><span class="hl-code">;
</span><span class="hl-identifier">txt2</span><span class="hl-code">=</span><span class="hl-quotes">&quot;</span><span class="hl-string">nice day</span><span class="hl-quotes">&quot;</span><span class="hl-code">;
</span><span class="hl-identifier">txt3</span><span class="hl-code">=</span><span class="hl-identifier">txt1</span><span class="hl-code">+</span><span class="hl-identifier">txt2</span><span class="hl-code">;</span></div>
</div>
<p>在以上语句执行后，变量 <em>txt3</em>包含的值是：</p>
<div class="example_code">
What a very nice day</div>
<br><a target="_blank" href="../try/try.php?filename=tryjs_operators3" class="tryitbtn" rel="noopener">尝试一下 »</a>
</div>

<p>或者把空格插入表达式中：:</p>

<div class="example">
<h2 class="example">实例</h2>
<div class="example_code">
<div class="hl-main"><span class="hl-identifier">txt1</span><span class="hl-code">=</span><span class="hl-quotes">&quot;</span><span class="hl-string">What a very</span><span class="hl-quotes">&quot;</span><span class="hl-code">;
</span><span class="hl-identifier">txt2</span><span class="hl-code">=</span><span class="hl-quotes">&quot;</span><span class="hl-string">nice day</span><span class="hl-quotes">&quot;</span><span class="hl-code">;
</span><span class="hl-identifier">txt3</span><span class="hl-code">=</span><span class="hl-identifier">txt1</span><span class="hl-code">+</span><span class="hl-quotes">&quot;</span><span class="hl-string"> </span><span class="hl-quotes">&quot;</span><span class="hl-code">+</span><span class="hl-identifier">txt2</span><span class="hl-code">;</span></div>
</div>
<p>在以上语句执行后，变量<em>txt3</em> 包含的值是：</p>
<div class="example_code">
What a very nice day</div>
<br><a target="_blank" href="../try/try.php?filename=tryjs_operators4" class="tryitbtn" rel="noopener">尝试一下 »</a>
</div>
<br><hr>
<h2>对字符串和数字进行加法运算</h2>

<p>两个数字相加，返回数字相加的和，如果数字与字符串相加，返回字符串，如下实例：</p>

<div class="example">
<h2 class="example">实例</h2>
<div class="example_code">
<div class="hl-main"><span class="hl-identifier">x</span><span class="hl-code">=</span><span class="hl-number">5</span><span class="hl-code">+</span><span class="hl-number">5</span><span class="hl-code">;
</span><span class="hl-identifier">y</span><span class="hl-code">=</span><span class="hl-quotes">&quot;</span><span class="hl-string">5</span><span class="hl-quotes">&quot;</span><span class="hl-code">+</span><span class="hl-number">5</span><span class="hl-code">;
</span><span class="hl-identifier">z</span><span class="hl-code">=</span><span class="hl-quotes">&quot;</span><span class="hl-string">Hello</span><span class="hl-quotes">&quot;</span><span class="hl-code">+</span><span class="hl-number">5</span><span class="hl-code">;</span></div>
</div>
<p><em>x</em>,<em>y</em>, 和 <em>z</em> 输出结果为:</p>
<div class="example_code">
10<br>
55<br>
Hello5</div>
<br><a target="_blank" href="../try/try.php?filename=tryjs_operators5" class="tryitbtn" rel="noopener">尝试一下 »</a>
</div>

<p> <b>规则:</b>如果把数字与字符串相加，结果将成为字符串！</p>			<!-- 其他扩展 -->
						
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		<li class="comment even thread-even depth-1" id="comment-11799"><span class="comt-f">#0</span><div class="comt-avatar wrapper"><i style="font-size:36px;" class="fa fa-user-circle" aria-hidden="true"></i><div class="tooltip"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;冰弦钰月</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;133***6556@qq.com</p></div><div id="runoobvote-id-11799" data-commid = "11799" class="upvotejs"><a class="upvote"></a> <span class="count">239</span></div></div><div class="comt-main" id="div-comment-11799"><pre>
var result1=5+5+"abc"; //结果将是"10abc"

var result2= ""+5+5+"abc"; //结果将是"55abc"
</pre><div class="comt-meta wrapper"><span class="comt-author"><a target="_blank" href="javascript:;">冰弦钰月</a><div class="tooltip tooltip1"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;冰弦钰月</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;133***6556@qq.com</p></div></span>6年前 (2017-05-09)</div></div></li><!-- #comment-## -->
<li class="comment odd alt thread-odd thread-alt depth-1" id="comment-13910"><span class="comt-f">#0</span><div class="comt-avatar wrapper"><i style="font-size:36px;" class="fa fa-user-circle" aria-hidden="true"></i><div class="tooltip"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;美芽</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;106***1206@qq.com</p></div><div id="runoobvote-id-13910" data-commid = "13910" class="upvotejs"><a class="upvote"></a> <span class="count">60</span></div></div><div class="comt-main" id="div-comment-13910"><p>空文本 <strong>+</strong> 数字得到的运算结果都是把数字转成字符串，无论文本有多少个空格。但是空格会计入长度。</p>
<pre>
var result1=""+5;         // 得到的结果是"5"

var result2=" "+5;        // 得到的结果是" 5"

var result3="       "+5;  // 得到的结果是"       5"</pre><div class="comt-meta wrapper"><span class="comt-author"><a target="_blank" href="javascript:;">美芽</a><div class="tooltip tooltip1"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;美芽</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;106***1206@qq.com</p></div></span>6年前 (2017-07-10)</div></div></li><!-- #comment-## -->
<li class="comment even thread-even depth-1" id="comment-15277"><span class="comt-f">#0</span><div class="comt-avatar wrapper"><i style="font-size:36px;" class="fa fa-user-circle" aria-hidden="true"></i><div class="tooltip"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;一一梦灬红尘</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;201***034203zwf@ncist.edu.cn</p></div><div id="runoobvote-id-15277" data-commid = "15277" class="upvotejs"><a class="upvote"></a> <span class="count">63</span></div></div><div class="comt-main" id="div-comment-15277"><pre>var result3="       "+5;  // 得到的结果是"       5"</pre>
<p>我想进一步解释, 图片说明：</p>

<p><img src="//www.runoob.com/wp-content/uploads/2017/07/js-html-space.jpg" /></p>

<p>html会压缩空格， 所以直观上显示的是字符串，没有显示空格。</p><div class="comt-meta wrapper"><span class="comt-author"><a target="_blank" href="javascript:;">一一梦灬红尘</a><div class="tooltip tooltip1"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;一一梦灬红尘</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;201***034203zwf@ncist.edu.cn</p></div></span>6年前 (2017-07-23)</div></div></li><!-- #comment-## -->
<li class="comment odd alt thread-odd thread-alt depth-1" id="comment-16274"><span class="comt-f">#0</span><div class="comt-avatar wrapper"><i style="font-size:36px;" class="fa fa-user-circle" aria-hidden="true"></i><div class="tooltip"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;GermanView`</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;282***579@qq.com</p></div><div id="runoobvote-id-16274" data-commid = "16274" class="upvotejs"><a class="upvote"></a> <span class="count">89</span></div></div><div class="comt-main" id="div-comment-16274"><p>常见的不同类型运算的转换方式：</p>

<p>1.字符串和数字相加，数字转成字符串.</p>

<pre>var one="This is a test";
var two=123;
var three=one+two;

// 结果：three:This is a test123</pre>

<p>2.数字和布尔值相加，布尔值 false 转成 0，true 转成 1</p>

<pre>var one=13;
var two=true;
var three=one+two;
// 结果 three:14</pre>

<p>3.字符串与布尔值相加，布尔值转化成字符串。</p>

<div class="comt-meta wrapper"><span class="comt-author"><a target="_blank" href="javascript:;">GermanView`</a><div class="tooltip tooltip1"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;GermanView`</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;282***579@qq.com</p></div></span>6年前 (2017-08-13)</div></div></li><!-- #comment-## -->
<li class="comment even thread-even depth-1" id="comment-16657"><span class="comt-f">#0</span><div class="comt-avatar wrapper"><i style="font-size:36px;" class="fa fa-user-circle" aria-hidden="true"></i><div class="tooltip"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;Roojay</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;roo***@126.com</p></div><div id="runoobvote-id-16657" data-commid = "16657" class="upvotejs"><a class="upvote"></a> <span class="count">91</span></div></div><div class="comt-main" id="div-comment-16657"><p>取模运算的结果符号只与左边值的符号有关：</p>

<pre>var x = 7 % 3; // 结果为 1
var y = 7 % (-3); // 结果为 1
var z = (-7) % 3; // 结果为 -1</pre>

<ul><li>
如果 % 左边的操作数是正数，则模除的结果为正数或零；
</li><li>
如果 % 左边的操作数是负数，则模除的结果为负数或零。
</li></ul><div class="comt-meta wrapper"><span class="comt-author"><a target="_blank" href="javascript:;">Roojay</a><div class="tooltip tooltip1"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;Roojay</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;roo***@126.com</p></div></span>6年前 (2017-08-21)</div></div></li><!-- #comment-## -->
<li class="comment odd alt thread-odd thread-alt depth-1" id="comment-19227"><span class="comt-f">#0</span><div class="comt-avatar wrapper"><i style="font-size:36px;" class="fa fa-user-circle" aria-hidden="true"></i><div class="tooltip"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;青妙</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;271***8654@qq.com</p></div><div id="runoobvote-id-19227" data-commid = "19227" class="upvotejs"><a class="upvote"></a> <span class="count">62</span></div></div><div class="comt-main" id="div-comment-19227"><p>数字与 null(空值) 相加，null 转化为数字 0：</p>

<pre>var car=null+3+4;    // 结果为7</pre>
<p>字符串与 null(空值) 相加，null 转化为字符串：</p>

<pre>var car=null+"a";    // 结果为 nulla</pre><div class="comt-meta wrapper"><span class="comt-author"><a target="_blank" href="javascript:;">青妙</a><div class="tooltip tooltip1"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;青妙</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;271***8654@qq.com</p></div></span>6年前 (2017-10-22)</div></div></li><!-- #comment-## -->
<li class="comment even thread-even depth-1" id="comment-24045"><span class="comt-f">#0</span><div class="comt-avatar wrapper"><i style="font-size:36px;" class="fa fa-user-circle" aria-hidden="true"></i><div class="tooltip"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;chenyy_jason</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;cyy***@126.com</p></div><div id="runoobvote-id-24045" data-commid = "24045" class="upvotejs"><a class="upvote"></a> <span class="count">33</span></div></div><div class="comt-main" id="div-comment-24045">JavaScript == 与 === 区别<p>1、对于 string、number 等基础类型，== 和 === 是有区别的</p><ul><li>a）不同类型间比较，== 之比较 "转化成同一类型后的值" 看 "值" 是否相等，=== 如果类型不同，其结果就是不等。</li><li>&nbsp;b）同类型比较，直接进行 "值" 比较，两者结果一样。</li></ul><p>2、对于 Array,Object 等高级类型，== 和 === 是没有区别的</p><p>进行 "指针地址" 比较</p><p>3、基础类型与高级类型，== 和 === 是有区别的</p><ul><li>a）对于 ==，将高级转化为基础类型，进行 "值" 比较</li><li>b）因为类型不同，=== 结果为 false</li></ul><div class="comt-meta wrapper"><span class="comt-author"><a target="_blank" href="javascript:;">chenyy_jason</a><div class="tooltip tooltip1"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;chenyy_jason</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;cyy***@126.com</p></div></span>5年前 (2018-02-09)</div></div></li><!-- #comment-## -->
<li class="comment odd alt thread-odd thread-alt depth-1" id="comment-49045"><span class="comt-f">#0</span><div class="comt-avatar wrapper"><i style="font-size:36px;" class="fa fa-user-circle" aria-hidden="true"></i><div class="tooltip"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;因为房价高，所以更需要努力</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;128***2546@qq.com</p></div><div id="runoobvote-id-49045" data-commid = "49045" class="upvotejs"><a class="upvote"></a> <span class="count">68</span></div></div><div class="comt-main" id="div-comment-49045"><p>1、字符串一个很能强大的数据类型；在执行加 <span class="marked">+</span> 时,将被加的对象统一处理为字符串。</p>
<p>2、bool 类型在与数字类型进行相加时，视为 0 或者 1 处理。</p>
<p>3、null 类型与数字类型进行累加时，视为 0 处理。</p>
<p>4、bool 类型与 null 类型进行累加时，视为其与整数类型累加处理。</p>
<p>5、undefined 除了与字符串进行累加时有效（undefined 视为字符串"undefined"处理），其他情况皆返回 NaN。</p>
<p>6、求模 <span class="marked">%</span> 运算，运算结果只取决于第一个数字的正负。</p>
<pre>-12 % -8 = -4; 
12 % -8 =  4;
-12 % 8 = -4;</pre>
<p>7、查看 String 数据类型支持的方法和属性：</p>

<p>打开网页后 F12 进行开发调试环境，找到 console 标签页面，执行：</p>

<pre>var str = new String('string');   
str 
</pre> 
<p>点开列表下拉箭头即可:</p>
<p><img src="https://www.runoob.com/wp-content/uploads/2019/12/30994114-FE40-416F-A993-F49210EF0374.jpg"></p><div class="comt-meta wrapper"><span class="comt-author"><a target="_blank" href="javascript:;">因为房价高，所以更需要努力</a><div class="tooltip tooltip1"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;因为房价高，所以更需要努力</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;128***2546@qq.com</p></div></span>3年前 (2019-12-05)</div></div></li><!-- #comment-## -->
<li class="comment even thread-even depth-1" id="comment-64606"><span class="comt-f">#0</span><div class="comt-avatar wrapper"><i style="font-size:36px;" class="fa fa-user-circle" aria-hidden="true"></i><div class="tooltip"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;数学</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;183***1835@qq.com</p></div><div id="runoobvote-id-64606" data-commid = "64606" class="upvotejs"><a class="upvote"></a> <span class="count">5</span></div></div><div class="comt-main" id="div-comment-64606"><p>空文本&nbsp;<strong>+</strong>&nbsp;数字得到的运算结果都是把数字转成字符串，无论文本有多少个空格。但是空格会计入长度。</p><pre>
var result1=""+5;         // 得到的结果是"5"

var result2=" "+5;        // 得到的结果是" 5"

var result3="       "+5;  // 得到的结果是"       5"
取模运算的结果符号只与左边值的符号有关：

var x = 7 % 3; // 结果为 1
var y = 7 % (-3); // 结果为 1
var z = (-7) % 3; // 结果为 -1
</pre><ul><li>&nbsp;如果 % 左边的操作数是正数，则模除的结果为正数或零；</li><li>&nbsp;如果 % 左边的操作数是负数，则模除的结果为负数或零。</li></ul><p>1、字符串一个很能强大的数据类型；在执行加&nbsp;+&nbsp;时,将被加的对象统一处理为字符串。</p><p>2、bool 类型在与数字类型进行相加时，视为 0 或者 1 处理。</p><p>3、null 类型与数字类型进行累加时，视为 0 处理。</p><p>4、bool 类型与 null 类型进行累加时，视为其与整数类型累加处理。</p><p>5、undefined 除了与字符串进行累加时有效（undefined 视为字符串"undefined"处理），其他情况皆返回 NaN。</p><div class="comt-meta wrapper"><span class="comt-author"><a target="_blank" href="javascript:;">数学</a><div class="tooltip tooltip1"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;数学</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;183***1835@qq.com</p></div></span>2年前 (2021-06-23)</div></div></li><!-- #comment-## -->
<li class="comment odd alt thread-odd thread-alt depth-1" id="comment-74899"><span class="comt-f">#0</span><div class="comt-avatar wrapper"><i style="font-size:36px;" class="fa fa-user-circle" aria-hidden="true"></i><div class="tooltip"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;virus</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;vis***ia_dignics@163.com</p></div><div id="runoobvote-id-74899" data-commid = "74899" class="upvotejs"><a class="upvote"></a> <span class="count">6</span></div></div><div class="comt-main" id="div-comment-74899"><p>字符串(<strong>string</strong>)类型和数字(<strong>number</strong>)类型进行加 <span class="marked">+</span> 运算会把 <strong>number</strong> 先隐式转换成 <strong>string</strong> 类型然后根据 <strong>string</strong> 的 <span class="marked">+</span> 运算规则进行字符串拼接，返回拼接后的字符串，由此得到 JavaScript独具特色的类型转换方式，例子如下：</p>

<pre>var x=1;
console.log(typeof x);
x=x+'';
console.log(typeof x);</pre>
<p>另外，补充一个类似的方法，如果要把字符串转换为数字，可以通过减 <span class="marked">-</span> 运算来进行，当然这里有一种情况，就是参与运算的 <strong>string</strong> 不能被转换成合法的 <strong>number</strong> 类型，那么最后结果就会返回 <strong>NaN</strong>。</p>

<pre>var x='1';
console.log(typeof x);
x=x-0;
console.log(typeof x);

var y='2';
y=y-1;
console.log(y);
var z='abc';
z=z-2;
console.log(z);</pre><div class="comt-meta wrapper"><span class="comt-author"><a target="_blank" href="javascript:;">virus</a><div class="tooltip tooltip1"><p><i class="fa fa-user" aria-hidden="true"></i>&nbsp;&nbsp;&nbsp;virus</p><p><i class="fa fa-envelope" aria-hidden="true"></i>&nbsp;&nbsp;vis***ia_dignics@163.com</p></div></span>8个月前 (08-29)</div></div></li><!-- #comment-## -->
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